带您了解Oracle层次查询

http://database.51cto.com/art/201010/231539.htm   Oracle层次查询(connect by )是结构化查询中用到的,下面就为您介绍Oracle层次查询的基本语法,希望可以让您对Oracle层次查询有更深的认识。 oracle中的select语句可以用START WITH...CONNECT BY PRIOR子句实现递归查询,connect by 是结构化查询中用到的,其基本语法是: select ... from <TableName> where <Conditional-1> start with <Conditional-2> connect by <Conditional-3> ; <Conditional-1>:过滤条件,用于对返回的所有记录进行过滤。 <Conditional-2>:查询结果重起始根结点的限定条件。 <Conditional-3>:连接条件 数据组织结构如下图:
数据库表结构如下: create table t2( root_id number, id number, name varchar(5), description varchar(10) ); insert into t2(root_id,id,name,description) values(0,1,'a','aaa'); insert into t2(root_id,id,name,description) values(1,2,'a1','aaa1'); insert into t2(root_id,id,name,description) values(1,3,'a2','aaa2'); insert into t2(root_id,id,name,description) values(0,4,'b','bbb'); insert into t2(root_id,id,name,description) values(4,5,'b1','bbb1'); insert into t2(root_id,id,name,description) values(4,6,'b2','bbb2'); 获取完整树: select * from t2 start with root_id = 0 connect by prior id = root_id;
获取特定子树: select * from t2 start with id = 1 connect by prior id = root_id;
select * from t2 start with id = 4 connect by prior id = root_id;
如果connect by prior中的prior被省略,则查询将不进行深层递归。 如: select * from t2 start with root_id = 0 connect by id = root_id;
select * from t2 start with id = 1 connect by id = root_id; 如:
posted @ 2014-06-17 15:32  adodo1  Views(123)  Comments(0Edit  收藏  举报